The present invention refers to a gas-dynamic pressure wave machine intended for supplying charge air to an internal combustion engine, comprising a rotor with cells, a low pressure fresh air inlet channel, a high pressure charge air channel leading to the internal combustion engine, a high pressure exhaust channel coming from the internal combustion engine, and a low pressure exhaust channel, the high pressure exhaust channel and the low pressure exhaust channel being enclosed in a gas enclosure and the low pressure fresh air inlet channel and the high pressure charge air channel being enclosed in an air enclosure, and the high pressure exhaust gas channel being provided on the rotor side with an enlargement.
A pressure wave machine of this kind is described in detail in WO 99/11914 to the applicant of the present invention, to which it is referred.
In a gas-dynamic pressure wave machine for supercharging internal combustion engines, operated with four channels and without additional control devices in the form of pockets, the process is only adjusted for a single operating point of the internal combustion engine. This is called the design point of the pressure wave machine. The use of so-called pockets in the enclosure walls allows a less tuning-sensitive design of the pressure wave machine and a significant extension of its load, speed, and volume range. The disadvantage of this method is an increase of the losses caused by secondary processes in the pockets, such as the inflow and outflow of the gases and the creation of pressure and expansion waves by the pockets.
The transition from the so-called primary process to the principal process, i.e. the tuned process, causes disturbances in the pressure wave process that lead to scavenging disruptions and thus to ranges of increased recirculation of exhaust gas into the charge air. In order to prevent an increased recirculation in these ranges as well as during starting, an inlet to the gas pocket, either in the form of a milled sill or of a controlled inlet must be provided, e.g. according to CH-A-681 738.
EP-B-885 352, for example, discloses a method allowing, in a standard pressure wave machine provided with a so-called wastegate flap, to divert excess high pressure exhaust gas, e.g. in the partial load range of the internal combustion engine, from the high pressure exhaust gas channel to the low pressure exhaust gas channel and thus to reduce the pressure upstream of the pressure wave machine. This will also reduce the pressure downstream of the pressure wave machine and thus the pressure in the intake channel of the internal combustion engine. However, in the absence of an inlet to the gas pocket, the opening of the wastegate will not only lead to the blowoff of the excess high pressure exhaust gas but also to a collapse of the scavenging of the rotor of the pressure wave machine. In the worst case, this may even cause a recirculation of the exhaust gas into the intake channel of the internal combustion engine, and in any event a significant deterioration of the compression efficiency of the pressure wave machine.
For example the previously mentioned applications CH-A-681 738 and EP-A-0 210 328 disclose a method according to which the exhaust gas expelled by the internal combustion engine allows to blow off the excess high pressure gas into the gas pockets through a bypass leading to the gas pocket of the pressure wave machine, thereby providing an improvement of the compression efficiency due to an improved scavenging of the rotor.
WO 99/11914 mentioned in the introduction in turn avoids the permanent use of a gas pocket and the resulting losses and eliminates the ridge between the exhaust gas channel and the gas pocket, which disturbs the pressure wave process when the inlet is open, as well as the energy losses in the form of flow and temperature losses caused by the geometry of the inlets to the gas pocket and the limitations in the design of the other channels.
However, the disadvantage of all these methods is that in the partial load range of the internal combustion engine, by blowing off the excess high pressure exhaust gas into the gas pockets or by enlarging the high pressure exhaust gas channel, the pressure in the high pressure exhaust gas channel still remains too high, i.e. the resulting negative pressure differential of charge air output of the pressure wave machine vs. high pressure exhaust gas supply to the pressure wave machine causes increased expulsion losses of the internal combustion engine and thus deteriorates the fuel efficiency in the partial load range of the internal combustion engine. At the same time, however, an undesired charging pressure subsists downstream of the pressure wave machine due to the insufficient reduction of the exhaust gas pressure in the pressure wave process. Furthermore, in a spark ignition engine with its load control by the throttle, this increased pressure in the intake must be additionally reduced by partially closing the throttle, thereby causing additional losses in the form of regulating losses.
The methods according to CH-A-681 738, EP-A-0 210 328, and WO 99/11914 for blowing off the excess high pressure gas have the disadvantage that the blowoff is insufficient in a wide range of the performance characteristics of the internal combustion engine, however mainly in the partial load range of the latter, i.e. the pressure upstream of the pressure wave machine is at a higher level than the pressure downstream of the pressure wave machine. The result is a negative pressure differential also across the internal combustion engine and thus an increase of the expulsion power required of the pistons of the internal combustion engine. In a spark ignition engine, due to the mixture control, the reduction of the excess pressure in the intake of the engine even requires a partial closure of the throttle, thereby causing additional losses in the form of regulating losses. Both of these loss factors have negative effects on the consumption of the internal combustion engine in partial load.